Twenty public-school janitors rake in more than $140,000 a year — far more than the teachers whose classrooms get tidied up, records show.

As The Post reported yesterday, suspected crooked custodian Trifon Radef counts himself among the rich elite, making more than $170,000 a year. Radef is under investigation for allegedly using city workers to renovate nine of the 10 properties he owns in Queens, officials say.

But Radef wasn’t even the highest-earning “custodial engineer.”

That honor went to Queens janitor Kevin Fitzgerald, who pulled in a whopping $181,643 at PS 229 in Woodside — thanks to the supplementary work he performed at two other Queens schools, records show.

Radef and Fitzgerald were among six custodians who took home more than $150,000 last year — and among the 20 who hauled in more than $140,000, the records show.

The janitors’ base salary maxes out at $106,329, according to their latest contract — about $6,000 more than the maximum salary for teachers.

“The idea that custodians make more than teachers is outrageous,” fumed former Schools Chancellor Harold O. Levy.

Head custodians can earn extra income in one of two ways, including through “temporary care” assignments at schools that don’t have a permanent custodial engineer. That work typically lasts less than two months but doesn’t require that janitors clock in beyond normal work hours.

Head janitors also can pad their pay by helping out at other schools on nights or weekends — which in Fitzgerald’s case nearly doubled his $92,100 base salary.

Radef, a 36-year veteran assigned to Roosevelt HS in The Bronx, earned an extra $53,000 last year by helping out evenings at Truman HS.

His former employees allege that he paid them with taxpayer funds to do work on nine of his Queens properties, valued at nearly $6 million, and that he created no-show jobs for pals.

City officials have been unsuccessfully trying to privatize at least some custodial services for decades but have run into legal hurdles and union opposition.

Levy hit the roof shortly after taking office in 2000 over the fact that custodial salaries topped those of teachers and some principals.

“It’s surprising to me that we still haven’t fixed the problem of custodians,” he told The Post yesterday. “Too many regard the buildings as private fiefdoms.”

Four years later, Mayor Bloomberg’s attempt to privatize services at more than 100 schools was defeated by a lawsuit filed by the Local 891 custodial union, which has 850 members.